1. Field of the Invention
The present invention relates to a pneumatic tire provided with a mark such as a letter, a numeral, a symbol and an emblem on a surface of a sidewall portion, more specifically to a pneumatic tire adapted to suppress a bend of a carcass layer, which is caused by a bias of a rubber quantity on a spot of the mark.
2. Description of the Related Art
On the surface of the sidewall portion of a pneumatic tire, provided are a letter, a numeral and a symbol that represent a manufacturer name, a tire type and the like and a mark such as an emblem representing a trademark. Generally, such a mark is formed convexly on the surface of the sidewall portion. And, a technique of enlarging the mark has been heretofore adopted for enhancing visibility (visuality) of the mark. However, when the mark is enlarged as described above, increased is a quantity of rubber flowing into a die concave portion for forming a mark, which is a part of planar rubber constituting the sidewall portion during tire vulcanization. Therefore, a thickness of the sidewall portion on the spot of the mark is thinned. Consequently, as shown in FIG. 7, in the vulcanized tire, there occurs a difference between a rubber thickness b of a sidewall portion 11 on a spot where a mark 12 is present and a rubber thickness a of the sidewall portion on a spot where the mark 12 is not present. In this case, the rubber thickness means a length from the surface of the sidewall portion 11 to a carcass layer 13. The difference described above causes a bend of the carcass layer 13 located under the mark 12 of the sidewall portion 11, leading to a problem that a carcass line cannot be uniformly maintained on a circumference thereof.
The object of the present invention is to provide a pneumatic tire capable of maintaining the carcass line approximately uniformly on the circumference thereof.
The present invention achieving the foregoing object is a pneumatic tire comprising: a carcass layer bridged between a pair of bead portions; and a convex mark provided on a surface of a sidewall portion, characterized in that a concave portion adjacent to the convex mark is provided on the surface of the sidewall portion, and a ratio of a volume v of the concave portion to a volume V of the convex mark is set as: 0.8Vxe2x89xa6vxe2x89xa61.2V.
Moreover, the present invention is a pneumatic tire comprising: a carcass layer bridged between a pair of bead portions; and a concave mark provided on a surface of a sidewall portion, characterized in that a convex portion adjacent to the concave mark is provided on the surface of the sidewall portion, and a ratio of a volume w of the convex portion to a volume W of the concave mark is set as: 0.8Wxe2x89xa6wxe2x89xa61.2W.
As described above, the concave portion is provided to be adjacent to the convex mark, and the volume ratio is regulated in the foregoing range. Therefore, even if the quantity of rubber flowing into the die concave portion for forming a mark during the tire vulcanization is increased, thinning of the thickness of the sidewall portion on the mark position as before can be avoided, and the thickness is not thickened too much because rubber having existed on the spot of the concave portion flows into a portion of the convex mark. Consequently, the bend of the carcass layer on the mark portion of the sidewall portion is suppressed, thus making it possible to maintain the carcass line approximately uniformly on the circumference thereof. The same can be applied to the case where the convex portion is provided to be adjacent to the concave mark.